The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.
Third and fourth generation mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architecture are able to support more sophisticated services than simple voice and messaging services offered by previous generations of mobile telecommunication systems. For example, with the improved radio interface and enhanced data rates provided by LTE systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile video conferencing that would previously only have been available via a fixed line data connection. The demand to deploy third and fourth generation networks is therefore strong and the coverage area of these networks, i.e. geographic locations where access to the networks is possible, is expected to increase rapidly.
The anticipated widespread deployment of third and fourth generation networks has led to the parallel development of a number of new infrastructure architectures involving a variety of classes of devices, of wireless access point units and of applications which may require different data rates, coverage areas or transmission powers. Unlike a conventional third or fourth generation communications device such as a smartphone, an MTC-type terminal is preferably relatively simple and inexpensive, having a reduced capability. Examples of recent developments include so-called machine type communication (MTC) applications, which are typified by semi-autonomous or autonomous wireless communication devices (i.e. MTC devices) communicating small amounts of data on a relatively infrequent basis. Examples include so-called smart meters which, for example, are located in a customer's house and periodically transmit information back to a central MTC server data relating to the customers consumption of a utility such as gas, water, electricity and so on. Other examples include relay nodes which provide assistance to local terminal communicating with a base station.
Whilst it can be convenient to have different systems addressing different needs from different mobile network users, the additions of new infrastructure and new services can also create an infrastructure problem, which is not desirable in a mobile network.
With the continuous growth in data transmitted in mobile networks, continually increasing network capacity comparatively is a problem faced by the industry. There are three parameters which can be changed in order to increase Radio Access network capacity: higher spectral efficiency, more radio spectrum and denser cell layout. The two former of these have limitations on the expected gains over today's LTE, and certainly improvements on the order of magnitude or more are not possible. Thus, in order to meet the stated 1000× capacity targets, small cells are getting a lot of attention [1].
In wideband wireless systems the bandwidth across which transmissions are scheduled is much wider than the coherence bandwidth of the physical medium. This means that the channel state may be very different in two or more sub-bands of the wideband operational bandwidth. For this purpose, when transmission are scheduled over wideband wireless systems some prior information on the channel state in frequency domain is necessary.
An objective technical problem addressed by the present disclosure, then, is to reduce latency and increase efficiency in a mobile communications network where the radio channel between infrastructure units may be very wide. This may be achieved through the employment of small cells and relay nodes, with the relay nodes able to estimate a state of the channel. This in itself has its own set of challenges to overcome.